1. Field of the Invention
The present invention relates to ink-jet recording inks suitable for ink-jet recording, methods for forming water-resistant images suitable for ink-jet recording, ink-jet recording inks for use in the methods, ink-jet recording apparatus, and imaged articles imaged by the apparatus.
2. Description of the Related Art
Certain inks for use ink-jet recording comprise a dye as a colorant, a moisturizer and water. Images formed from these dye inks, however, have insufficient water resistance upon imaging on recording media such as recording paper. Particularly, when images are formed on plain paper using these inks, they have significantly low water resistance. Such plain paper is commercially available, is intended mainly to be used in electrophotographic copiers and is not optimized in its structure, composition and properties for use in ink-jet recording.
To increase water resistance in printing on plain paper, Japanese Patent Application Laid-Open (JP-A) No. 02-296878 and No. 02-255876 each disclose a water-based ink composition comprising a polyamine. However, in the ink, a salt of a hydrophilic moiety of the dye is formed, and the dye has decreased solubility, thus inviting nozzle clogging, decreased reliability, bronzing (association of the dye) on a printed matter, uneven printing and/or insufficient density.
JP-A No. 03-91577 discloses an ink composition. The ink composition includes a dye containing a carboxyl group with an ammonium salt group or volatile substituted ammonium salt group, in which ammonia or amine vaporizes and the carboxyl group is converted into a free acid on a recording medium to thereby produce an image with good water resistance. The dye shows good solubility in early stages but shows decreasing solubility with gradual vaporization of the ammonia or amine from the ink, thus often inviting nozzle clogging or decreased stability of ink.
As a possible solution to this problem, JP-A No. 10-212439, No. 11-293167, No. 11-315231 and No. 2002-265829 each disclose a technique of improving the water resistance of an image on a recording medium, by incorporating an organosilicon compound into an ink. The organosilicon compound is prepared by hydrolyzing a hydrolyzable silane compound having a nitrogen-containing organic group or its partial hydrolysate with a hydrolyzable silane compound or its partial hydrolysate.
According to this technique, the organosilicon compound undergoes polycondensation when an ink droplet is applied to a recording medium and water in the ink droplet vaporizes or penetrates into the recording medium, and the polycondensed organosilicon compound surrounds the dye. Thus, even when the resulting image on the recording medium gets wet with water, the dye does not bleed out into water, and the image has improved water resistance.
However, black inks among such conventional inks comprising the organosilicon compound fade after long-term storage. The fading is remarkable particularly in black inks containing an azo black dye. While its detailed mechanism has not been clarified, the fading occurs probably because the organosilicon compound attacks the azo bond of the azo black dye after long-term storage to thereby reduce the azo dye.
C. I. Acid Red 289 has high saturation, is useful as a magenta dye but does not show sufficiently high water resistance even with the use of the organosilicon compound. Hereinabove and hereinafter, “C. I.” stands for color index. When an image formed from the ink gets wet, a magenta color bleeds out around the image.
The conventional inks comprising the organosilicon compound are also susceptible to their pH changes. Even when these inks are adjusted to basic in their preparation, their pH changes due to elution from ink tanks, degradation of the ink materials, or influence from the surroundings. The pH change induces precipitation, which in turn invites clogging of nozzle heads in an ink-jet printer. This is because such a dye used in an ink-jet ink is generally anionic and aggregates due to the pH change as a result of the incorporation of the organosilicon compound. This is also true for a pigment ink, because a pigment therein is dispersed stably generally by action of an anionic group adsorbed by or chemically bonded with the pigment.